Improved soil fertility increases nodulation of Phaseolus beans
1992
Lupwayi, N.Z. | Mkandawire, A.B.C.
The effect of soil fertility on the response of field beans (Phaseolus vulgaris L.) to inoculation with Rhizobium leguminosarum bv. phaseoli was investigated at five sites in northern and central Malawi. A split-plot design consisting of (a) un-inoculated plants, (b) inoculated plants and (c) N-fertilized plants as main-plot treatments and (i) low fertility (no additional nutrients applied) and (ii) high fertility (P, S, and Mo applied) was adopted. Nodulation was highest at Sokola (84 nodules per plant) and lowest on an acid soil at Lunyangwa (11 nodules per plant). There was no significant response (p more than 0.05) in nodule number to inoculation at all sites, i.e., un inoculated plants formed as many nodules as inoculated plants. This is indicative of a large population of indigenous rhizobia in the soils, which implies that competition for nodulation between inoculant and indigenous rhizobia is probably an important factor in response to inoculation. Improved soil fertility increased nodule number by up to 500 percent,probably by stimulating multiplication of rhizobia in the bean root rhizosphere. However, improved nodulation was translated into a significant increase in grain yield only at Champhira, where correlation between nodule number and grain yield was also significant (r = 0.72, p less than 0.01).
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